Sana'a: A massive blackout has darkened large swaths of Yemen just as Muslims were sitting down to break their dawn-to-dusk fast for the holy month of Ramadan.

The Electricity Authority says the outage is due to a grid failure caused by heavy rain.

Officials say millions were without power for most of Monday night in the capital and other major cities.

In the southern port of Aden, crowds blockaded roads with barricades of burning tires to demand authorities restore power. Some shouted anti-government slogans, reflecting the sentiments of the south's secessionist movement.

The officials spoke on condition of anonymity because they are not authorized to speak to the press.

The cut occurred as temperatures hovered about 38 degree Celsius.